The variability in the amplitudes of the lunar semidiurnal tide was investigated using maps of total electron content over Brazil from January 2011 to December 2014. Long-period variability showed that the annual variation is always present in all investigated magnetic latitudes, and it represents the main component of the temporal variability. Semiannual and triannual (two and three times a year, respectively) oscillations were the second and third components, respectively, but they presented significant temporal and spatial variability without a well-defined pattern. Among the short-period oscillations in the amplitude of the lunar tide, the most pronounced ones were concentrated between 7–11 d. These oscillations were stronger around the equinoxes, in particular between September and November in almost all latitudes. In some years, as in 2013 and 2014, for instance, they appeared with a large power spectral density in the winter hemisphere. These observed short-period oscillations could be a result of a direct modulation of the lunar semidiurnal tide by planetary waves from the lower atmosphere and/or due to electrodynamic coupling of E and F regions of the ionosphere.

中文翻译：

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巴西电离层月半日潮汐振幅的变化

使用2011年1月至2014年12月在巴西的总电子含量图调查了月半日潮的振幅变化。长期变化表明，所有调查的磁纬度始终存在年变化，这是主要的时间变异性的组成部分。半年和三年一次的振荡（分别为每年两次和三次）分别是第二和第三次振荡，但是它们呈现出明显的时间和空间变异性，没有明确的模式。在潮汐幅度的短期振荡中，最明显的振荡集中在7-11 d之间。这些振动在春分点附近更明显，尤其是在几乎所有纬度的9月到11月之间。几年来 例如，与2013年和2014年一样，它们在冬季半球出现的功率谱密度很大。这些观测到的短时振荡可能是来自低层大气的行星波直接调制月半日潮的结果和/或由于电离层E和F区的电动力耦合。